1. Field of the Invention
The present invention relates to a new and improved variable orifice plate for controlling the flow in coal pipes supplying burners in furnaces and boilers. More particularly, the present invention is directed to an orifice plate mounted in a coal pipe and movable between alternate positions to vary the effective flow cross-section for controlling the flow of primary coal and air to a burner. By adjusting the angle of tilt of the orifice plate relative to the general direction of flow along a coal pipe, the effective flow cross-section through the orifice opening is varied and adjustments can be made while on-line during operation of a burner so that the effects of position settings are rapidly available and easily tabulated without requiring the burner to be shut down. 2. Background of the Prior Art
There has been an historical problem of obtaining balanced pulverized coal flow in multiple coal pipe distribution systems. Typically, coal pipes are manifolded from the discharge of a pulverizer. A manifold can be in the form of a classifier, a flow splitter or a riffle box. Previously, a method used to equalize coal flow to each burner was to throttle each coal line to obtain equal pressure drops through all of the multiple coal lines. Because of the nature of two phase flow, including solid pulverizer coal and primary air, several iterations of throttling action were often required to obtain even a temporary coal line balance of plus or minus 10% of the average flow rate in each pipe. Because of the increased need to maintain good coal flow with low NO.sub.X firing, typical previous trial and error methods have not worked.
A new and improved variable orifice plate for coal pipes in accordance with the present invention is useful in a wide variety of pulverized coal supply systems having multiple coal pipes and is especially well adapted for use in systems for supplying multiple burners of all types of furnaces including "TURBO" furnaces such as that shown and described in U.S. Pat. No. 4,517,904, incorporated herein by reference and sold by the assignee herein under the trademark "TURBO" .sub.R.
U.S. Pat. No. 1,477,824 discloses a powdered material firing apparatus employing cylindrically-shaped air valve positioned upstream from the point of coal introduction into the stream.
U.S. Pat. No. 1,708,496 discloses a pulverized fuel burner employing rotatably mounted solid circular damper disks in separate fuel and air conduits connected to supply the burner.
U.S. Pat. No. 2,079,420 discloses a burner for firing furnaces with pulverized coal wherein a pair of semi-circular-shaped valves are provided at the inlet end of the burner for dividing the flow between separate nozzle sections.
U.S. Pat. No. 3,002,472 discloses a comminution system for wet solid materials (coal) including generally circular dampers in coal and air pipes feeding a steam generating unit.
U.S. Pat. No. 4,459,922 discloses an externally adjustable pipe orifice assembly employing pivoted plates.